The present invention is related to U.S. Pat. No. 4,775,133 assigned to the assignee of the present invention.
The present invention relates to an electrically actuated air valve for use in an air distribution system wherein the volume of conditioned air supplied to a zone is varied in order to control the temperature within the zone.
One of the currently most favored types of building ventilation systems is the variable air volume system wherein a central source provides conditioned air for distribution to various zones within a building via a network of ducts. Since heating and cooling requirements vary from zone to zone, and within individual zones depending upon factors such as solar load and the nature of zone usage, it is necessary that provision be made to selectively control the amount of conditioned air supplied to a zone in response to local demand.
In a variable air volume system, the selective delivery of conditioned air to a particular zone is accomplished through the association of at least one air distribution box with each zone. Such air distribution boxes define supply plenums and include one or more air outlets in communication with the zone. Additionally, each box has an airflow control valve, for varying the volume of air delivered into the plenum and, therefore, into the zone. Such air valves are controlled by a thermostat in the zone so as to supply the proper volume of conditioned air to maintain or achieve a selected zone temperature.
The present invention is directed to an electric motor driven air valve for use in variable air volume air distribution systems. The most common type of electrically driven air valve is that shown and taught in U.S. Pat. No. 4,082,114, to Hantke et al., which is assigned to the assignee of the present invention. The valve of the Hantke patent includes a closed ended cylindrical portion downstream of the valve inlet in which a generally tubular valve member is disposed for movement axially of the valve housing. The size of a series of radial ports, and therefore the flow of air through the valve, is determined by the position of the valve member within the cylindrical, closed ended valve housing.
The valve of the Hantke design is relatively complex and is, as well, somewhat expensive of manufacture. Additionally, dedicated sealing means are required at each peripheral edge of the tubular valve member in order to completely shutoff airflow through the valve. Although not detailed in the Hantke patent, the de-energization of the valve motor is based upon the physical contact of a portion of the damper assembly, subsequent to the movement of a portion of the assembly into contact with a limit switch.
U.S. Pat. No. 4,775,133 referred to above, discloses an electric motor driven air valve having a physically movable, spring biased backplate. In response to the abutment of the valve damper with a fixed inlet seating surface the backplate of the valve of the aforementioned application is driven away from the valve inlet until such time as contact with a limit switch is made which de-energizes the motor. The motor continues to drive the valve damper into the seating surface even after the initial abutment of the valve damper with its seat, until the limit switch is made.
The arrangement of the aforementioned patent succeeds in the prevention of motor stalling subsequent to the abutment of the valve damper and inlet seating surface but is successful at the cost of having to provide for the physical movement and biasing of the valve backplate. The arrangement contemplates the spring loading of the backplate and the provision of limit switches to control motor operation. It will be appreciated that variations among mechanical components and in the assembly/manufacturing process as well as damage to the relatively delicate limit switches can affect the reliability of the valve when such switches are employed.
The need continues to exist for an electric motor driven air valve which is relatively uncomplicated and inexpensive of manufacture yet which provides for the precise control of the volume of air flowing through the valve and is capable of tight, controlled closure in a manner not susceptible to mechanical binding and/or motor stalling.
The present invention is therefore directed generally to an electric motor driven air valve which is commercially practicable and which employs the development of strain in a valve component, subsequent to valve closure, to control the energization and de-energization of the drive motor.